1. Field of the Invention
The present invention relates to an engine cylinder head in which water jackets and an exhaust gas recirculation passage are formed therein, the engine exhaust gas recirculation passage opening into an exhaust passage at one end and opening into a side surface of an intake side at the other end thereof.
2. Description of the Related Art
It is a common practice to re-circulate a part of exhaust gases from combustion chambers to an intake system path in order to reduce oxides of nitrogen in exhaust gases from the engine. Known as an exhaust gas recirculation passage (hereinafter, referred to as EGR passage) of this type is an exhaust gas recirculation passage drilled in the interior of a cylinder head so as to open to immediately after exhaust ports in a combustion chamber at an upstream end thereof (JP-A-63-143754U).
However, when exhaust gases taken out from immediately after the exhaust ports are recirculated to the intake side by way of the relatively short EGR passage, as illustrated in the above Japanese Utility Model Unexamined Publication, high temperature exhaust gases flow into the intake passage. This can cause early deterioration of an EGR valve or setting of oil and gasoline in blow-by gases in a tar-like fashion to thereby narrow the passage.
It is known to externally attach a cooling device for cooling recirculation gases, but this prevents engines from being made compact and is disadvantageous in cost.
The invention was made with a view to solving the problems inherent in the prior art technologies, and a main object thereof is to provide an engine cylinder head which can not only secure a sufficient cooling capacity for re-circulating exhaust gases but also is improved such that no reduction in rigidity of the cylinder head is caused, even if an EGR passage is formed therein.
With a view to attaining the object, according to a first aspect of the invention, there is provided an engine cylinder head in which a water jacket (10) and an EGR passage (12) are formed therein, the EGR passage (12) opening into an exhaust passage (7) at one end and opening into a side of an intake side at the other end thereof, the engine cylinder being characterized in that the EGR passage is provided outwardly in a cylinder arrangement direction of head bolt pass-through holes (9) formed in one end of the engine cylinder head in the cylinder arrangement direction.
According to this construction, the EGR passage can be made much longer and moreover the EGR passage can be provided without head bolts being spaced apart from the combustion chamber.
According to a second aspect of the invention, there is provided an engine cylinder head as set forth in the first aspect of the invention, wherein at least a part (a downstream side portion 12b in an embodiment) of the EGR passage is formed in a wall (a thick portion 13 in the embodiment) constituting the water jacket, and wherein ribs (15) are provided on a portion of the wall where the EGR passage extends in such a manner as to protrude into the water jacket.
According to this construction, since the ribs function as heat radiating fins, the cooling efficiency can be improved, and moreover an improvement in the rigidity of the cylinder head with the ribs can be attempted.
According to a third aspect of the invention, there is provide an engine cylinder head as set forth in the first or second aspect of the invention, wherein the EGR passage is contiguous with boss portions (11) where the head bolt pass-through holes are formed.
According to this construction, no reduction in the rigidity of the cylinder head has to be called for even if the EGR passage is formed in the cylinder head.
According to a fourth aspect of the invention, there is provided an engine cylinder head in which a water jacket and an exhaust gas recirculation passage are formed therein, the exhaust gas recirculation passage opening into an exhaust passage at one end and opening into a side of an intake side at the other end thereof, the engine cylinder being characterized in that the cylinder head comprises a plurality of exhaust ports in each combustion chamber, and wherein the one end of the exhaust gas recirculation passage opens into a collecting portion (14) of exhaust passages extending from the plurality of exhaust ports, respectively.
According to this construction, the length of the passage can be made far longer than that in the cylinder head in which the EGR passage is made to open in a side which is closer to the combustion chamber than the collecting portion.